Chemically modified asphalts are receiving widespread commercial use especially in the areas of highway maintenance and repair. As used herein, the term "highway maintenance and repair" includes not only the repair and maintenance of highways and roads but also contemplates, within its scope, such structures as driveways, parking lots, airport runways and like vehicular supporting surfaces, and also contemplates, within its scope, waterproofing of bridge decks. Exemplary of such chemically modified asphalt compositions are those produced by reacting asphalt, a vinyl aromatic monomer and a rubbery or elastomeric polymer, as set forth example in U.S. Pat. No. 4,273,685, which is hereby incorporated by reference. Such types of compositions have been employed for minimizing reflective cracking, for joint and crack sealing purposes, for bridge deck waterproofing and for pothole repair. These compositions may be employed as is or, if desired, glass fibers may be dispersed therein. In highway repair and maintenance, for purposes of minimizing reflective cracking, cracks may first be filled with such chemically modified asphalt compositions, and then the crack overlaid with a fibrous reinforcement material, preferably a glass fiber reinforcing material, and the reinforcing material then overcoated with a hot application of such chemically modified asphalts.
While chemically modified asphalts, which are produced by reacting a paving grade asphalt, a vinyl aromatic monomer and a rubber or elastomeric polymer, have many outstanding properties making them well adapted for applications indicated above, such formulations need to be improved with respect to their resistance to thermal degradation and with respect to their low temperature flexural strength properties.
Compared to such chemically modified asphalts, wherein the asphalt employed is an AC-20 paving grade asphalt, the present invention provides compositions which have increased resistance to thermal degradation and improved low temperature flexural strengths, and which can be synthesized in a shorter period of time. That is, ingredients employed in the present invention generally show enhanced reaction kinetics compared to the use of an AC-20 paving grade asphalt. Essentially, the present invention is a chemically modified asphalt composition comprising the reaction product of a high oil asphalt, a vinyl aromatic monomer and a rubbery, or elastomeric, polymer.